BluetoothMetrics: Add Bluetooth U protos

Metric Design Review: https://eldar.corp.google.com/assessments/152668825/revisions/8#sections/999001
Bug: 267371667
Test: make

Change-Id: I1f793cbc22cf0bf1ae03c8ee56f5b9c0bc00ab80
Merged-In: I1f793cbc22cf0bf1ae03c8ee56f5b9c0bc00ab80
(cherry picked from commit 8289a08486badfcd964298507ebcba39e992b649)